Mice of the BALB/c strain injected with a line of the syngeneic T cell lymphoma S-49 which grows in suspension accept the tumor and die within two weeks. BALB/c mice injected with a plastic adherent (7.3) line of the same tumor are not killed. Furthermore, mice injected first with the 7.3 line and subsequently challenged with TAS are protected from the syngeneic tumor.